The evolution of wireless communication over the past century, since Guglielmo Marconi's 1897 demonstration of radio's ability to provide continuous contact with ships sailing the English Channel, has been remarkable. Since Marconi's discovery, new wireline and wireless communication methods, services and standards have been adopted by people throughout the world. This evolution has been accelerating, particularly over the last ten years, during which the mobile radio communications industry has grown by orders of magnitude, fueled by numerous technological advances that have made portable radio equipment smaller, cheaper and more reliable. The exponential growth of mobile telephony will continue to rise in the coming decades as well, as this wireless network interacts with and eventually overtakes the existing wireline networks.
One advance in the telecommunications arts is the use of phase digitization, i.e., measuring the phase of a signal and reporting the result as a number. Phase digitization is similar to analog-to-digital conversion, where the amplitude of a signal is measured and the result reported as a digital number. Although originally conceived in military and satellite communications, phase digitizers are currently used in all types of telecommunications, e.g., in land mobile radio (LMR). In the United States, cellular channels are spaced 30 KHz apart, permitting large deviation modulating schemes. In the land mobile radio spectrum, channel spacing is 25 KHz in the 800 MHZ range and 12.5 KHz in other ranges, e.g., 400 MHZ, 900 MHZ, etc. As is understood in the art, phase digitizers operate best in wide band operation, and their performance degrades as the channel deviation decreases. Since the Federal Communications Commission (FCC) plans to migrate spectrum usage to even narrower spacing in the near future, phase digitizer performance degradation due to reduced deviation will become an increasing concern and may seriously compromise system performance.
As is understood in the art, the performance problem in narrow band phase digitizer operation is the result of an inherent flaw that arises from the slightly non-periodic sampling of the phase digitizer. In other words, phase digitization of signals results in unpredictable signal artifacts. For example, when a phase digitizer is used as a demodulator in FM systems, demodulation of a pure tone causes extra tones to appear. Energy from the original signal is converted to the extra tones by the non-periodic sampling of the phase digitizer. The net result is that the measured hum and noise of an FM system employing a phase digitizer is worse than an FM system using an analog discriminator. Similarly, when a phase digitizer is used in phase modulation schemes, phase error increases, resulting in higher bit error rates.
One proposed solution addressing the quantization and sampling problems is averaging the phase samples, which would improve the performance of phase digitizing systems. One such solution is set forth in U.S. Pat. No. 5,220,275 to Bo P. Holmqvist. Another is to error compensate by interpolation, as described in U.S. patent application Ser. No. 08/982,202, entitled "Phase Digitizer for Radio Communications", also to Mr. Holmqvist.
It is, however, difficult to efficiently average phase and interpolate, primarily due to the non-linear wrapping of phase around the zero degree point.
What is needed, therefore, is an efficient way to average digitized phase samples that ameliorates or eliminates the aforementioned inherent flaws.
It is, accordingly, an object of the present invention to improve the efficiency of averaging phase digitizer samples.
It is also an object of the present invention to employ an improved system and method that overcomes or reduces the deleterious effects caused by the inherent flaws encountered in phase digitization.